• Muthukumaran Nirmala

      Articles written in Journal of Chemical Sciences

    • Design and synthesis of ruthenium(II) OCO pincer type NHC complexes and their catalytic role towards the synthesis of amides

      Muthukumaran Nirmala Periasamy Viswanathamurthi

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      The present contribution describes the synthesis and characterization of a family of robust ruthenium complexes, supported by a tridentate pincer ligand of the type bis-phenolate-𝑁-heterocyclic carbene [𝑡Bu(OCO)2−] (NHC). Ruthenium(II) complexes (1-3) bearing bis-phenolate-𝑁-heterocyclic carbene ligand were synthesized in good yields by the reaction of imidazolinium proligand (HL) with metal precursors [RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3 or Py) by transmetalation from the corresponding silver carbene complex. All the Ru(II)-NHC complexes have been characterized by elemental analyses, spectroscopic methods as well as ESI mass spectrometry. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The tridentate nature of the 𝑡Bu(OCO)2− ligand as well as some level of steric protection provided by the 𝑡Bu groups may rationalize the excellent stability of the Ru-Ccarbene bond in the present systems. Moreover, for the explorations of catalytic potential of the synthesized compounds, all the three [Ru-NHC] complexes (1-3) were tested as catalysts for amidation of alcohols with amines. Notably, the complex 1 was found to be very efficient and versatile catalyst towards amidation of a wide range of alcohols with amines.

    • Ruthenium(II) complexes bearing pyridine-functionalized N-heterocyclic carbene ligands: Synthesis, structure and catalytic application over amide synthesis

      MUTHUKUMARAN NIRMALA PERIASAMY VISWANATHAMURTHI

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      A series of four imidazolium salts was synthesized by the reaction of 2-bromopyridine with 1- substituted imidazoles. These imidazolium salts (1a–d) were successfully employed as ligand precursors for the syntheses of new ruthenium(II) complexes bearing neutral bidentate ligands of N-heterocyclic carbene and pyridine donor moiety. The NHC-ruthenium(II) complexes (3a–d) were synthesized by reacting the appropriately substituted pyridine-functionalized N-heterocyclic carbenes with Ag₂O forming the NHC–silver bromide in situ followed by transmetalation with [RuHCl(CO)(PPh₃)₃]. The new complexes were characterized by elemental analyses and spectroscopy (IR, UV-Vis, ¹H, ¹³C, ³¹P-NMR) as well as ESI mass spectrometry. Based on the spectral results, an octahedral geometry was assigned for all the complexes. The complexes were shown to be efficient catalysts for the one-pot conversion of various aldehydes to their corresponding primary amides with good to excellent isolated yields using NH₂OH.HCl and NaHCO₃. The effects of solvent, base, temperature, time and catalyst loading were also investigated. A broad range of amides were successfully synthesized with excellent isolated yields using the above optimized protocol. Notably, the complex 3a was found to be a very efficient and versatile catalyst towards amidation of a wide range of aldehydes.

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